1. Field of the Invention
This invention relates to a transferring device for transferring an article between plural vacuum chambers in an CVD device, an etching device, a sputtering device, an inspection device, etc. used to manufacture an electronic device such as a semiconductor integrated circuit.
2. Description of Related Art
Transferring devices have been conventionally designed to include in a vacuum chamber a cylindrical bulkhead (partition wall) having a rectangular cross-section or a cylindrical bulkhead having a circular cross-section in which both of a thick portion and a thin portion coexist as shown in FIG. 3. In both of the transferring devices, the atmospheric state at the inner peripheral surface side 1a of the bulkhead is maintained. A float member 3 having a transferring rod is disposed at the outer peripheral surface side 1b of the bulkhead while a main body 4 of the transferring device is provided at the inner peripheral surface side of the bulkhead. The main body 4 of the transferring device includes a magnetic bearing at the outer peripheral portion 4a thereof, and is so designed as to be reciprocatively moved between both ends of the bulkhead. The magnetic bearing comprises plural electromagnets 10 and 11 and a sensor portion. The sensor portion detects the floating position of the float member, and each electromagnet is excited on the basis of a detection value which is outputted from the sensor portion. Through this operation, magnetism acts on the float member through the bulkhead to support the float member. In the transferring device as described above, the float member is supported by the magnetic bearing in a magnetically floating state, and when the main body of the transferring device is reciprocatively moved, the magnetically-supported float member is also reciprocatively moved in synchronism with the reciprocative motion of the main body. As a result, the transferring rod of the float member serves to transfer an article.
However, in such a conventional transferring device, the bulkhead is deformed due to a pressure difference between the outer peripheral surface side of the bulkhead (vacuum) and the inner peripheral surface side (air atmosphere) in a case where the bulkhead is designed in a cylindrical shape having a rectangular cross-section. This deformation can be prevented by forming the bulkhead to be thicker. If the thickness of the bulkhead is increased, the magnetic force acting on the float member from an electromagnet through the bulkhead is weakened, and thus it is required to increase exciting current of the electromagnet. Therefore, there occur disadvantages that the power consumption of the device becomes increased, and that the whole device is heated. On the other hand, in a device having a cylindrical bulkhead having a circular cross-section (in place of the cylindrical bulkhead having a rectangular cross-section as described above), low power consumption and prevention of the heating of the device can be achieved by decreasing the thickness of a portion of the bulkhead which confronts the electromagnet and increasing the thickness of another portion of the bulkhead which does not confront the electromagnet. However, it is difficult to produce such a circular-cross-sectional cylindrical bulkhead having a variable thickness. Further, the size in the vertical direction of the device is increased because support portions 15 and 16 must be provided at the lower portion of the bulkhead, and the rigidity of the device is weakened because an opening portion is provided at the lower portion of the float member. If the rigidity of the device is increased, there would occur various problems that the device must be designed in large-scale and greater weight, and that the exciting current must be increased.